Because of certain deficiencies of presently available methods of cooling tissue-containing paraffin blocks during or immediately before their being cut, a new method of cooling the blocks was developed. It consists of "bathing" the paraffin block during the process of cutting in cooled air evaporated from dry ice contained in a container which is mounted on a microtome and which overhangs the mounted paraffin block. Perforations in the floor of the overhanging portion of the container and closure of the top of the container allows evaporation of the dry ice over the mounted paraffin block with uniform cooling of the block. The quality of histologic sections has been improved by this new method of cooling of paraffin blocks.